The invention relates to a vehicle seat belt system.
Vehicle seat belt systems conventionally include a retractor from which a belt can be withdrawn for use against the tension of a retractor spring. So that the belt holds the user in his seat during an emergency, the retractor locks against belt withdrawal, usually in response to excessive belt acceleration and/or in response to excessive acceleration (which term is used herein to include, where appropriate, deceleration) of the vehicle, and thus of the retractor mounted in the vehicle.
In certain circumstances, the sensitivity of the retractor necessary to ensure locking in emergency conditions can have disadvantageous consequences. An example occurs in respect of seat belt systems used in the cabins of large commercial road vehicles. Such cabins have a certain freedom of movement relative to the chassis of the vehicle, so that even under normal driving conditions, the cabin, and thus the retractor, undergoes relatively high levels of acceleration. These accelerations can be sufficient to cause locking of the retractor in circumstances where restraint of the user by the belt is not needed. This restraint can be inconvenient, for example, in restricting the driver in carrying out movements necessary to the control of the vehicle.
The seat belt system may be a "passive" one, that is, one which is arranged to come into use without the user being required to take any action specifically for the purpose. For example, the system may be such that the belt is applied to the occupant of a vehicle seat under mechanical or electrical power as a consequence of his sitting down in the seat. When such a system has a retractor with a retractor acceleration sensitive locking mechanism, it can happen that locking occurs when the vehicle is parked on an inclined and/or as a consequence of retractor movement when a person enters or leaves the cabin. Locking in these circumstances also is undesirable as movement into and out of the seat and/or proper functioning of the passive system may be hindered or prevented. Such undesirable locking can occur in such circumstances with retractors which lock in response to retractor acceleration even where the system is not a passive one.
All these circumstances discourage use of the seat belt, or where the system is a passive one, encourage attempts to evade its use.
It is therefore an object of the invention to provide a seat belt system including a retractor which locks against belt withdrawal in response to a predetermined acceleration condition, in which undesired locking is prevented in a simple way without diminution of the protection which the system affords.
It is also an object of the invention to provide a simple and convenient means for inhibiting locking of an acceleration sensitive emergency locking seat belt retractor in response to spurious accelerations.
It is a further object of the invention to provide, in a vehicle having a seat belt system including an acceleration sensitive locking retractor, means inhibiting locking of the retractor unless the vehicle experiences an emergency acceleration condition.
It is an additional object of the invention to provide a seat belt system including a retractor, in which inadvertent locking of the retractor is overcome in response to a door opening operation.